Subversion Repositories Games.Chess Giants

/*

  Stockfish, a UCI chess playing engine derived from Glaurung 2.1

  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)

  Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad

  Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad

  Stockfish is free software: you can redistribute it and/or modify

  it under the terms of the GNU General Public License as published by

  the Free Software Foundation, either version 3 of the License, or

  (at your option) any later version.

  Stockfish is distributed in the hope that it will be useful,

  but WITHOUT ANY WARRANTY; without even the implied warranty of

  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License

  along with this program.  If not, see <http://www.gnu.org/licenses/>.

*/

#include <cassert>

#include "movepick.h"

#include "thread.h"

namespace {

  enum Stages {

    MAIN_SEARCH, CAPTURES_INIT, GOOD_CAPTURES, KILLERS, COUNTERMOVE, QUIET_INIT, QUIET, BAD_CAPTURES,

    EVASION, EVASIONS_INIT, ALL_EVASIONS,

    PROBCUT, PROBCUT_INIT, PROBCUT_CAPTURES,

    QSEARCH_WITH_CHECKS, QCAPTURES_1_INIT, QCAPTURES_1, QCHECKS,

    QSEARCH_NO_CHECKS, QCAPTURES_2_INIT, QCAPTURES_2,

    QSEARCH_RECAPTURES, QRECAPTURES

  };

  // Our insertion sort, which is guaranteed to be stable, as it should be

  void insertion_sort(ExtMove* begin, ExtMove* end)

  {

    ExtMove tmp, *p, *q;

    for (p = begin + 1; p < end; ++p)

    {

        tmp = *p;

        for (q = p; q != begin && *(q-1) < tmp; --q)

            *q = *(q-1);

        *q = tmp;

    }

  }

  // pick_best() finds the best move in the range (begin, end) and moves it to

  // the front. It's faster than sorting all the moves in advance when there

  // are few moves, e.g., the possible captures.

  Move pick_best(ExtMove* begin, ExtMove* end)

  {

      std::swap(*begin, *std::max_element(begin, end));

      return *begin;

  }

} // namespace

/// Constructors of the MovePicker class. As arguments we pass information

/// to help it to return the (presumably) good moves first, to decide which

/// moves to return (in the quiescence search, for instance, we only want to

/// search captures, promotions, and some checks) and how important good move

/// ordering is at the current node.

MovePicker::MovePicker(const Position& p, Move ttm, Depth d, Search::Stack* s)

           : pos(p), ss(s), depth(d) {

  assert(d > DEPTH_ZERO);

  Square prevSq = to_sq((ss-1)->currentMove);

  countermove = pos.this_thread()->counterMoves[pos.piece_on(prevSq)][prevSq];

  stage = pos.checkers() ? EVASION : MAIN_SEARCH;

  ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;

  stage += (ttMove == MOVE_NONE);

}

MovePicker::MovePicker(const Position& p, Move ttm, Depth d, Square s)

           : pos(p) {

  assert(d <= DEPTH_ZERO);

  if (pos.checkers())

      stage = EVASION;

  else if (d > DEPTH_QS_NO_CHECKS)

      stage = QSEARCH_WITH_CHECKS;

  else if (d > DEPTH_QS_RECAPTURES)

      stage = QSEARCH_NO_CHECKS;

  else

  {

      stage = QSEARCH_RECAPTURES;

      recaptureSquare = s;

      return;

  }

  ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;

  stage += (ttMove == MOVE_NONE);

}

MovePicker::MovePicker(const Position& p, Move ttm, Value th)

           : pos(p), threshold(th) {

  assert(!pos.checkers());

  stage = PROBCUT;

  // In ProbCut we generate captures with SEE higher than the given threshold

  ttMove =   ttm

          && pos.pseudo_legal(ttm)

          && pos.capture(ttm)

          && pos.see_ge(ttm, threshold + 1)? ttm : MOVE_NONE;

  stage += (ttMove == MOVE_NONE);

}

/// score() assigns a numerical value to each move in a move list. The moves with

/// highest values will be picked first.

template<>

void MovePicker::score<CAPTURES>() {

  // Winning and equal captures in the main search are ordered by MVV, preferring

  // captures near our home rank. Surprisingly, this appears to perform slightly

  // better than SEE-based move ordering: exchanging big pieces before capturing

  // a hanging piece probably helps to reduce the subtree size.

  // In the main search we want to push captures with negative SEE values to the

  // badCaptures[] array, but instead of doing it now we delay until the move

  // has been picked up, saving some SEE calls in case we get a cutoff.

  for (auto& m : *this)

      m.value =  PieceValue[MG][pos.piece_on(to_sq(m))]

               - Value(200 * relative_rank(pos.side_to_move(), to_sq(m)));

}

template<>

void MovePicker::score<QUIETS>() {

  const HistoryStats& history = pos.this_thread()->history;

  const FromToStats& fromTo = pos.this_thread()->fromTo;

  const CounterMoveStats* cm = (ss-1)->counterMoves;

  const CounterMoveStats* fm = (ss-2)->counterMoves;

  const CounterMoveStats* f2 = (ss-4)->counterMoves;

  Color c = pos.side_to_move();

  for (auto& m : *this)

      m.value =      history[pos.moved_piece(m)][to_sq(m)]

               + (cm ? (*cm)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)

               + (fm ? (*fm)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)

               + (f2 ? (*f2)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)

               + fromTo.get(c, m);

}

template<>

void MovePicker::score<EVASIONS>() {

  // Try captures ordered by MVV/LVA, then non-captures ordered by history value

  const HistoryStats& history = pos.this_thread()->history;

  const FromToStats& fromTo = pos.this_thread()->fromTo;

  Color c = pos.side_to_move();

  for (auto& m : *this)

      if (pos.capture(m))

          m.value =  PieceValue[MG][pos.piece_on(to_sq(m))]

                   - Value(type_of(pos.moved_piece(m))) + HistoryStats::Max;

      else

          m.value = history[pos.moved_piece(m)][to_sq(m)] + fromTo.get(c, m);

}

/// next_move() is the most important method of the MovePicker class. It returns

/// a new pseudo legal move every time it is called, until there are no more moves

/// left. It picks the move with the biggest value from a list of generated moves

/// taking care not to return the ttMove if it has already been searched.

Move MovePicker::next_move() {

  Move move;

  switch (stage) {

  case MAIN_SEARCH: case EVASION: case QSEARCH_WITH_CHECKS:

  case QSEARCH_NO_CHECKS: case PROBCUT:

      ++stage;

      return ttMove;

  case CAPTURES_INIT:

      endBadCaptures = cur = moves;

      endMoves = generate<CAPTURES>(pos, cur);

      score<CAPTURES>();

      ++stage;

  case GOOD_CAPTURES:

      while (cur < endMoves)

      {

          move = pick_best(cur++, endMoves);

          if (move != ttMove)

          {

              if (pos.see_ge(move, VALUE_ZERO))

                  return move;

              // Losing capture, move it to the beginning of the array

              *endBadCaptures++ = move;

          }

      }

      ++stage;

      move = ss->killers[0];  // First killer move

      if (    move != MOVE_NONE

          &&  move != ttMove

          &&  pos.pseudo_legal(move)

          && !pos.capture(move))

          return move;

  case KILLERS:

      ++stage;

      move = ss->killers[1]; // Second killer move

      if (    move != MOVE_NONE

          &&  move != ttMove

          &&  pos.pseudo_legal(move)

          && !pos.capture(move))

          return move;

  case COUNTERMOVE:

      ++stage;

      move = countermove;

      if (    move != MOVE_NONE

          &&  move != ttMove

          &&  move != ss->killers[0]

          &&  move != ss->killers[1]

          &&  pos.pseudo_legal(move)

          && !pos.capture(move))

          return move;

  case QUIET_INIT:

      cur = endBadCaptures;

      endMoves = generate<QUIETS>(pos, cur);

      score<QUIETS>();

      if (depth < 3 * ONE_PLY)

      {

          ExtMove* goodQuiet = std::partition(cur, endMoves, [](const ExtMove& m)

                                             { return m.value > VALUE_ZERO; });

          insertion_sort(cur, goodQuiet);

      } else

          insertion_sort(cur, endMoves);

      ++stage;

  case QUIET:

      while (cur < endMoves)

      {

          move = *cur++;

          if (   move != ttMove

              && move != ss->killers[0]

              && move != ss->killers[1]

              && move != countermove)

              return move;

      }

      ++stage;

      cur = moves; // Point to beginning of bad captures

  case BAD_CAPTURES:

      if (cur < endBadCaptures)

          return *cur++;

      break;

  case EVASIONS_INIT:

      cur = moves;

      endMoves = generate<EVASIONS>(pos, cur);

      score<EVASIONS>();

      ++stage;

  case ALL_EVASIONS:

      while (cur < endMoves)

      {

          move = pick_best(cur++, endMoves);

          if (move != ttMove)

              return move;

      }

      break;

  case PROBCUT_INIT:

      cur = moves;

      endMoves = generate<CAPTURES>(pos, cur);

      score<CAPTURES>();

      ++stage;

  case PROBCUT_CAPTURES:

      while (cur < endMoves)

      {

          move = pick_best(cur++, endMoves);

          if (   move != ttMove

              && pos.see_ge(move, threshold + 1))

              return move;

      }

      break;

  case QCAPTURES_1_INIT: case QCAPTURES_2_INIT:

      cur = moves;

      endMoves = generate<CAPTURES>(pos, cur);

      score<CAPTURES>();

      ++stage;

  case QCAPTURES_1: case QCAPTURES_2:

      while (cur < endMoves)

      {

          move = pick_best(cur++, endMoves);

          if (move != ttMove)

              return move;

      }

      if (stage == QCAPTURES_2)

          break;

      cur = moves;

      endMoves = generate<QUIET_CHECKS>(pos, cur);

      ++stage;

  case QCHECKS:

      while (cur < endMoves)

      {

          move = cur++->move;

          if (move != ttMove)

              return move;

      }

      break;

  case QSEARCH_RECAPTURES:

      cur = moves;

      endMoves = generate<CAPTURES>(pos, cur);

      score<CAPTURES>();

      ++stage;

  case QRECAPTURES:

      while (cur < endMoves)

      {

          move = pick_best(cur++, endMoves);

          if (to_sq(move) == recaptureSquare)

              return move;

      }

      break;

  default:

      assert(false);

  }

  return MOVE_NONE;

}